[llvm] [DirectX] add support for i64 buffer load/stores (PR #145047)

[Justin Bogner via llvm-commits]

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@@ -570,22 +575,54 @@ static bool expandTypedBufferLoadIntrinsic(CallInst *Orig) {
     ExtractElements.push_back(
         Builder.CreateExtractElement(Extract, Builder.getInt32(I)));
 
-  // combine into double(s)
+  // combine into double(s) or int64(s)
   Value *Result = PoisonValue::get(BufferTy);
   for (unsigned I = 0; I < ExtractNum; I += 2) {
-    Value *Dbl =
-        Builder.CreateIntrinsic(Builder.getDoubleTy(), Intrinsic::dx_asdouble,
-                                {ExtractElements[I], ExtractElements[I + 1]});
+    Value *Combined = nullptr;
+    if (IsDouble) {
+      // For doubles, use dx_asdouble intrinsic
+      Combined =
+          Builder.CreateIntrinsic(Builder.getDoubleTy(), Intrinsic::dx_asdouble,
+                                  {ExtractElements[I], ExtractElements[I + 1]});
+    } else {
+      // For int64, manually combine two int32s
+      // First, zero-extend both values to i64
+      Value *Lo = Builder.CreateZExt(ExtractElements[I], Builder.getInt64Ty());
+      Value *Hi =
+          Builder.CreateZExt(ExtractElements[I + 1], Builder.getInt64Ty());
+      // Shift the high bits left by 32 bits
+      Value *ShiftedHi = Builder.CreateShl(Hi, Builder.getInt64(32));
+      // OR the high and low bits together
+      Combined = Builder.CreateOr(Lo, ShiftedHi);
+    }
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bogner wrote:

Might be worth pulling this out into a function? `createCombined64Bit(IRBuilder, Value *, Value *)` or something like that.

https://github.com/llvm/llvm-project/pull/145047